San Antonio is in a very interesting area. It is right on the line between the gardener's 8 and 9 zones, it sits at the foot of the hill country, east is farmland and west is almost semi-arid. We are still fairly humid here, which surprised me, being from east texas. I thought it would be dryer, but we still get moisture from the gulf of mexico.
I don't know the exact answer to your question, although I can say that not too far east of san antonio the trees change. Probably 100 miles or so east and it looks different already. I don't really recall any mesquites closer to houston than that.
I got this mesquite from a tree service guy.
I met another tree service person not far from where I live. He has agreed to dump all his logs and chips on my property for free. He asked if I wanted one or ten loads a week.
He says he is cutting a lot of ash right now. It will be interesting to see what comes out of the back of his truck.
Also, he said that a farmer plows in the chips to replenish the minerals in his soil. I have 26 acres with very poor soil, so I'm planning on doing that with all his chips. Hopefully I can get free logs and turn my soil around too. That would be great if I were able to do that for free.